Inorganic-organic hybrid materials obtained by introducing an organic group in between the layers/voids of inorganic layered materials have the potential to demonstrate the characteristics that cannot be achieved by an individual host or guest. Grafting reactions occur by establishing covalent bonds between the reactive groups of the layer and an adequate reactant molecule, which ensures greater chemical, structural, and thermal stability for the compound. Recently, many examples of surface modified silica, glasses and zeolite-like porous materials involving covalent bond formation with organo silanes have been widely investigated. [A. Kulak, Y. J. Lee, Y. S. Park, K. B. Yoon, Angew. Chem. Int. Ed. 5 (2000) 950; K. C. Vrancken, L. De Coster, P. Van Der Voort, P. J. Grobet, E. I. Vansant, J. Colloid. Interface Sci. 170 (1995) 71; S. Y. Choi, Y. J. Lee, Y. S. Park, K. Ha, K. B. Yoon, J. Am. Chem. Soc. 122 (2000) 5201]. LDH is ubiquitous, economical and non-toxic powder having a high anion exchange capacity, good adsorbent, swelling, and intercalation properties. These profitable features of anionic clay make it useful in the move towards establishing environmental friendly catalyst [B. M. Chaudhary, M. L. Kantam, V. Neeraj, K. K. Rao, F. Figureras, L. Delotte, Green Chem. 3 (2001) 257]. Due to the above exiting properties different anionic surfactant, metal complexes and enzymes have been incorporated via an electrostatic force of attraction [S. Bhattacharjee, J. A. Anderson Chem. Commun., (2004) 554.; E. Gardner, T. J. Pinnavaia, Appl. Catal., 167 (1998) 65; B. M. Choudary, S. Madhi, N. S. Chowdari, M. L. Kantam, B. Sreedhar, J. Am. Chem. Soc. 124 (2002) 14127; S. Bhattacharjee and J. A. Anderson, Catalysis Letters. 95 (2004) 119; S. Gago, M. Pillinger, A. A. Valente, T. M. Santos, J. Rocha, and I. S. Goncalves, Inorg. Chem. 43 (2004) 5422]. But till date studies on covalent attachment of organic moieties (APTES) in LDH, which can enhance the catalytic activity of LDH have never been explored.
This invention particularly relates to an eco-friendly process employing recyclable LDH-APTES as a heterogeneous catalyst in place of soluble bases for Aldol condensation, Knoevenagel condensation, Henry reaction and Michael addition. This present invention provides an interlayer surface modified LDH with organic moieties through covalent bonding. This technique involves the insertion of long chain anionic surfactant into LDH host, which offers a gentle way of expanding the interlayer space of LDH. That will make the layered material more compatible with the intercalated organic moiety.
Reference may be made to US patent U.S. Pat. No. 4,458,026 wherein aldol condensation of acetone is carried out by heat-treated synthetic anionic clay. The inherent disadvantage in this process is higher temperatures and longer reaction time with lower yields. Reference may be made to Choudary et al., Tetrahedron, 56 (2000) 9357 wherein Knoevenagel condensation and Michael addition is carried out by Mg—Al—O-t-Bu hydrotalcite. The inherent disadvantage in this process is the catalyst is more sensitive to moisture. Reference may be made to Choudary et al., Green. Chem., (1999) 187 wherein Henry reaction is carried out by Mg—Al rehydrated hydrotalcite. The inherent disadvantages in the process are low yields, longer reaction time and require activation for each catalytic cycle to reuse. Hence to avoid these above problems, we demonstrate for the first time a process that provides an innovative mean of consistent activity for several cycles in C—C bond forming reactions at room temperature. This makes the process economical and possible for commercial realisation. Therefore, LDH/APTES is better alternative for of base catalyze reactions. Thus this invention offers the best techno-economic route for the synthesis of intermediates in the preparation of drugs, pharmaceuticals and fine chemicals.